Looking at the literal geographical/geological idea of a continent (humour me here), Eurasia is clearly one rather than two. The northernmost stretch of the Europe-Asia border are the Ural mountains, 600 miles of which we traversed by ski. The Urals are the world’s oldest extant range and formed from tectonic jostling over 250 million years ago. It wasn’t a collision of landmasses either side of a shrinking sea, as famously with the Himalayas. It was eons of frottage between three already joined tectonic landmasses within the super continent of Pangaea.
The other five continents could all be argued to inhabit their own current tectonic plate. However, if we are to use defunct tectonic plates as continental boundaries, then things get very complicated with many, many continents to consider. Even if we are to use current plates as a guide then Far East Russia and much of Japan relocates to “North America”, Iceland snaps in twain, and the Philippines get their own shiny new ring on the Olympic flag. Silly isn’t it?